[jumpy]

Ok. First impressions wasn't happy with some of the buttons going to different places, then realised stop/refresh was in a better location.
Overall I like having a cleaner space with the orange FF menu popout, one row of buttons/address bar with tabs underneath then web page down to windows taskbar.
Like the Tab colours. It's now easier to see which tab is current, before, not so much. Not used the tab groups thing yet, but I'm sure it will come in handy sooner or later (been using speed dial plugin in a similar manner before).

So far so good - though I did have a fatal error in windows active desktop (associated with having a webpage as your desktop according to the resultant reboot error - though I have never used it). This happened the same day I installed FF4, but it could be a coincidence.
Not noticeably faster imo, most probably for a number of reason not related to browser performance.

Apart from messing about with a separate profile and install location + shortcut target to try and keep v3.6, it all seemed simple enough when I decided to update properly.